In order to inactivate viruses possibly contaminating a plasma protein such as albumin, Murray et al. proposed a process which comprises heating an aqueous solution of said protein (hereinafter referred to as liquid heating) (cf. The New York Academy of Medicine, 31 (5), 341-358 (1955)). This liquid heating process has been believed to be a very effective virus inactivation method and the effect of the same in the inactivation of a virus has been epidemiologically proved. Thus, liquid heating has been routinely employed up to the present time.
Among plasma proteins, however, only a few including albumin can withstand the above-mentioned liquid heating process and many of those showing high physiological or biological activities are highly sensitive to heat and liable to be thermally denatured, which frequently causes a decrease or loss in activity.
Fibrinogen, which is a plasma protein, is frequently accompanied by a risk of contamination with virus(es), in particular, hepatitis or AIDS virus. Therefore, it should be heated to inactivate these viruses. However, fibrinogen is unstable to heat and thus inactivated during the conventional liquid heating process. Therefore, it has been desired to provide a process for heating fibrinogen to thereby inactivate viruses contaminating the same without inactivating the fibrinogen per se.